Hot Rods Regular/Hand Warming Packs literally "run on air". Simply open to activate. Hot Rods Hand Warmers keep you warm all day. Each pair (1100-2R) can be slipped into Hot Rods Winter Liners, Winter Accessories, or your gloves. Regular Warming Packs last up to 11 hours with an average temperature of 135*F/57*C. No shaking to activate.